Unraveling Results from Comparable Demand and Supply: An Experimental Investigation

by Muriel Niederle, Alvin E. Roth and M. Utku Unver

Executive Summary —
In many professional labor markets, most entry-level hires begin work at around the same time: for example, soon after graduating from college or graduate or professional school. Despite a common start time, offers can be made and contracts can be signed at any time prior to the start of employment, sometimes well over a year before employment will begin. "Unraveling" happens in markets in which competition for the elite firms and workers is fierce, but the quality of workers may not be reliably revealed until after a good deal of hiring has already been completed. Thus unraveling is sometimes a cause of market failure, particularly when contracts come to be determined before critical information is available. In this paper Muriel Niederle of Stanford, Alvin E. Roth of HBS, and M. Utku Ünver of Boston College consider conditions related to supply and demand that tend to facilitate or mitigate unraveling. Key concepts include:

It is commonly suggested by economists and lay participants in markets that unraveling results from competition related to an imbalance of demand and supply.

Unraveling can have many causes, because markets are multidimensional and time is only one-dimensional (and so transactions can only move in two directions in time, earlier or later). So there can be many different reasons that make it advantageous to make transactions earlier.

When looking at a labor market, it is not uncommon for participants on both sides of the market to be nervous about their prospects, and it can be difficult to be sure which is the short side of the market. Even in a market with more applicants than positions there may be a shortage of the most highly qualified applicants.

Attempts to prevent or reverse unraveling are often a source of new market design in the form of new rules or market institutions.

Author Abstract

Markets sometimes unravel, with offers becoming inefficiently early. Often this is attributed to competition arising from an imbalance of demand and supply, typically excess demand for workers. However this presents a puzzle, since unraveling can only occur when firms are willing to make early offers and workers are willing to accept them. We present a model and experiment in which workers' quality becomes known only in the late part of the market. However, in equilibrium, matching can occur (inefficiently) early only when there is comparable demand and supply: a surplus of applicants, but a shortage of high quality applicants.
48 pages